1. Field of the Invention
Certain solid propellants, tracer compositions, incendiaries, flares, and other pyrotechnics are made from solid inorganic or organic oxidizers, metal fuels, and binders. While the specific compositions vary depending on end use characteristics, they all have in common the basic ingredients of oxidizer, metal fuel, and binder. In certain applications, these compositions must be adjusted or modified to obtain burning rates which are higher than those obtainable by ordinary combustion processes. Oftentimes, the burning rates of these materials have been increased by use of combustion modifiers or burning rate catalysts, but these additives have the disadvantage of increasing the sensitivity of the resultant composition towards friction, heat, impact, or electrostatic discharge.
2. Description of the Prior Art
Ferrocene compounds and various metal oxides have been used in the past for increasing the burning rates of these compositions. Another means of increasing the burning rates of these materials is through the incorporation of metallic fibers within the composition. These metallic fibers are added so as to provide a means of conducting heat from the combustion zone into the burning composition. One of the difficulties encountered in the use of such metallic fibers is the problem associated with the alignment of the fibers. During casting and loading operations the flow patterns of the composition provide non-uniform distribution of metallic fibers which causes uneven and irregular burning during the combustion process. As a result, the use of fibers as a means of conducting heat into the composition has never reached the desired level of proficiency.
Other attempts to achieve greater influx of heat from the combustion zone to the surface of the composition have involved making intimate mixtures of the metal powder (magnesium or aluminum) and oxidizer powder in order to try to force the metal combustion to occur as close as possible to the surface of the composition. These attempts have been largely unsuccessful, and graphic evidence is available. High speed motion pictures showing these compositions undergoing combustion shows aluminum particles leaving the surface of the composition and igniting at some finite distance away from the surface, thereby depriving the surface of heat which would allow the composition to burn at a higher rate.
In order to overcome the problems with regard to obtaining good combustion of the aluminum powder very near the surface of the composition the instant invention deals with a manner of treating the solid ammonium perchlorate oxidizer so as to cause aluminum metal to be combusted at or very near the surface of the composition, thereby providing a greater heat release in the critical area, resulting in increases in the composition burning rate. This result is produced by using an aluminum coated ammonium perchlorate in a binder, as opposed to a mere mixture of aluminum and ammonium perchlorate.
Oxidizers other than ammonium perchlorate have been coated in the past, U.S. Pat. No. 3,120,459 and 3,535,172, to produce more stable oxidizers, but the use of the coated oxidizers, especially ammonium perchlorate, to control, modify, or in any way effect the burning rate has not been heretofore disclosed.